Weak charge-ordering behavior in phase separated (Ln1/3Sm2/3)2/3Ca1/3MnO3 (Ln = Pr and La) manganites

We have studied a weak charge-ordering behavior in phase separated (Ln(1/3)Sm(2/3))(2/3)Ca1/3MnO3 (Ln = Pr and La) manganites with same hole doping but slightly different tolerance factors. The M(T) and p(T) curves of the Pr-sample showed an anomaly caused by a weak charge-order (CO) transition at similar to 210 K. while that of La-sample did not. However, the La-sample displayed a weak anomaly related to the CO instability in the derivative curve of the temperature dependent magnetoresistance. This result is understood on the basis that the CO phase in La-sample is partly suppressed by a large magnetic field of similar to 80 kOe, while in Pr-sample it is not collapsed in that field scale. Our data support the existence of charge-ordering, electronic phase separation and a field-induced reduction of weak CO instability for La-sample, which can contribute towards high MR especially at lower temperatures due to partial melting of CO phase and/or percolation behavior. (c) 2007 Elsevier Ltd. All rights reserved.